Fabrication of etched foils for electrolytic capacitors



Nov. 10, 1959 b. ALTENPOHL ETAL I 2,912,369 FABRIGATION OF ETCHED FOILS FOR ELECTROLYTIC CAPACITORS I Filed July 27, 1955 INVENTORS. DIETRICH ALTENPOHL 8| FRIEDRICH EMLER BY 'w/ dl,

United States Patent FABRICATION OF ETCHED FOILS FOR ELECTROLYTIC CAPACITORS Dietrich Alteupohl and Friedrich Ernler, Singen (Hohentwiel), Germany, assignors to Aluminium-Waltzwerke Singen G.m.b.H., Singen (Hohentwiel), Germany, a German company Application July 27, 1955, Serial No. 524,784

Claims priority, application Germany July 28, 1954 2 Claims. (Cl.204-33) It is known that often the surface of aluminum bodies especially the surface of aluminum foils with a thickness of 0.1 mm. are etched by chemical or electrolytic processes to increase their active surface area. Such etched foils are used after a forming (oxidizing) process in the fabrication of electrolytic capacitors. In many cases an utmost increase of the surface area is required. This can only be attained by a highly fissured and rugged surface. In the process of making such a surface it is inevitable that several particles loose their connection with the metal base, because the tops of the formed peaks break up or because little grains of the metallic structure are loosened.

Such loose aluminum particles are easily discovered, for example by rubbing the etched foil with the naked hand or with a cloth.

Careful investigations of etched foils which were unsatisfactory after the formation (electrolytic oxidation), showedthat the loose particles on the surface were responsible for the unsatisfactory condition of the etched foils. It has been discovered that this unsatisfactory condition is due to the fact that the oxide film grows beneath the loose particles into the metallic base. In consequence loose aluminum particles lie afterwards in the capacitor on the negative side of the dielectric oxide film which detach electrons and therefore decrease considerably the rectifying effect of the thermionic valve.

According to the invention these disadvantages are avoided and therefore the etched foil appreciably improved in its effect by removing mechanically the loose particles from the surface of the foil before forming it. This removing can be carried out in different ways. For example after the etching process, in which is attained for example a five fold increase of the surface area, the foil is first rinsed in a water bath or by spraying and afterwards rubbed on both sides with wet wipers of foamed latex, whereby the loose particles are removed completely or at least nearly completely from the surface. Advantageously one uses rotating rolls of foamed latex. Besides rubbing, the foamed latex has also a sucking effect which contributes to the thorough removing of the loose particles. Instead of foamed latex of course other natural or synthetic products with a same effect may be used, or the sucking effect may be produced in another way.

It is also advantageous to use perforated metal rolls which are coated with foamed latex and which are flowed through by a rinsing liquid from the inside to the outside.

Removing the loose particles is also possible by spraying water or blowing a gas against the surface of the foil with a high pressure. But the use of foamed latex wipers is more eflicacious.

The accompanying drawing shows schematically an 2,912,369 Patented Nov. 10, 1959 example of an arrangement for removing the loose particles from the surface of an etched aluminum foil.

The etched foil 1 passes first the tank 2, where it is drawn through the rinsing water 3 and sprayed with water or blown by gas under pressure from the nozzle 4. The reference numeral 5 designates the rolls which guide the foil 1. After leaving the tank 2 the wet foil is rubbed with the rolls 6 and 7 of foamed latex. It is also possible to arrange two pairs of rolls from which the first pair chiefly loosens the particles and the second pair removes them from the surface of the foil.

Using the described apparatus it proved to be possible to fabricate an etched foil with at least a five fold increase of the surface area which shows an appreciable higher quality in spite of the highly fissured surface. The improvement in the quality of capacitors the electrodes of which have been treated according to our invention are shown by the following results:

p (1) Residual current of a capacitor with an etched and formed aluminum foil without removing the loose particles: 0.2 ma.

(2) Residual current of a capacitor with the same etched foil, rubbed with two pairs of wet rolls of foamed latex to remove the loose particles before forming: 0.09 ma.

The residual current had been measured at 450 volts in the finished capacitor.

We claim:

1. In a method of making aluminum electrodes for electrolytic capacitors comprising the steps of etching the surface of the aluminum electrode to multiply the effective surface area of the electrode, rinsing the etched surface with'a liquid to remove any soluble salts from the etched surface and oxidizing the etched surface of the electrode, the improvement comprising subjecting the etched surface of the aluminum electrode prior to the oxidizing step to the action of a soft, porous, rotating roll, which action subjects the etched surfaceto the suction of the roll, to remove any particles loosened during the etching step from the surface of the aluminum elec-. trode before the oxidizing step, which particles would normally not be dislodged by the rinsing action alone.

2. In a method of making aluminum electrodes for electrolytic capacitors comprising the steps of etching the surface of an aluminum electrodev to multiply the effective surface area of the electrode and oxidizing the surface of the electrode after the etching step, the improvement comprising the steps of removing any particles loosened during the etching step from the surface of the aluminum electrode before the oxidizing step by subjecting the said surface to the action of a soft, porous foam latex rotatable roll, said roll having a hollow interior which communicates with a liquid under pressure and perforations from the hollow interior to the outer periphery of the roll through which the liquid flows, the action of the rotatable roll subjecting the etched surf-ace to the combined action of the suction of the roll and the rinsing liquid.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,946 Treuhaft et al. Apr. 24, 1951 2,682,502 Hesch June 29, 1954 2,684,922 Pollock July 27, 1954 FOREIGN PATENTS 467,024 Great Britain June 9, 1937 

1. IN A METHOD OF MAKING ALUMINUM ELECTRODES FOR ELECTROLYTIC CAPACTIORS COMPRISING THE STEPS OF ETCHING THE SURFACE OF THE ALUMINUM ELECTRODE TO MULTIPLY THE EFFECTIVE SURFACE AREA OF THE ELECTRODE, RINSING THE ETCHED SURFACE WITH A LIQUID TO REMOVE ANY SOLUBLE SALTS FROM THE ETCHED SURFACE AND OXIDIZING THE ETECHED SURFACE OF THE ELECTRODE, THE IMPROVEMENT COMPRISING SUBJECTING THE ETCHED SURFACE OF THE ALUMINUM ELECTRODE PRIOR TO THE OXIDIZING STEP TO THE ACTION OF A SOFT, POROUS, ROTATING ROLL, WHICH ACTION SUBJECTS THE ETCHED SURFACE TO THE SUCTION OF THE ROLL, TO REMOVE ANY PARTICLES LOOSENED DURING THE ETCHING STEP FROM THE SURFACE OF THE ALUMINUM ELEC- 